Unraveling the iron deficiency responsive proteome in <i>Arabidopsis </i>shoot by iTRAQ-OFFGEL approach

Iron (Fe) is required by plants for basic redox reactions in photosynthesis and respiration, and for many other key enzymatic reactions in biological processes. Fe homeostatic mechanisms have evolved in plants to enable the uptake and sequestration of Fe in cells. To elucidate the network of proteins that regulate Fe homeostasis and transport, we optimized the iTRAQ-OFFGEL method to identify and quantify the number of proteins that respond to Fe deficiency in the model plant Arabidopsis. In this study, Fe deficiency was created using Fe-deficient growth conditions, excess zinc (Zn), and use of the irt1-1 mutant in which the IRT1 Fe transporter is disrupted. Using the iTRAQ-OFFGEL approach, we identified 1139 proteins, including novel Fe deficiency-responsive proteins, in microsomal fractions isolated from 3 different types of Fe-deficient shoots compared with just 233 proteins identified using conventional iTRAQ-CEX. Further analysis showed that greater numbers of low-abundance proteins could be identified using the iTRAQ-OFFGEL method and that proteins could be identified from numerous cellular compartments. The improved iTRAQ-OFFGEL method used in this study provided an efficient means for identifying greater numbers of proteins from microsomal fractions of Arabidopsis shoots. The proteome identified in this study provides new insight into the regulatory cross talk between Fe-deficient and excess Zn conditions.